Bingo is a long popular and widely played games familiar to most people. Basically the game is played on cards divided into squares, the majority of squares each being identified by its own letter-number combination (e.g. B-9, I-36, etc). Different cards have differently identified squares. The game operator calls out the series of randomly selected letter-number combinations. Each player puts a marker on any square identified by the then called letter-number combination, on any of his cards. Achieving a predetermined pattern of markers on a card wins the game.
Charitable, civic and the like groups commonly stage bingo games as fund raisers open to the public. A typical group-sponsored bingo evening may draw several hundred people, many of whom simultaneously play several bingo cards. For the convenience of the game operator and to assure random selection of the letter-number combinations, various letter-number selecting mechanisms have been used in such bingo contests. Commonly, each letter-number combination is printed on an article such as a Ping-Pong ball, the balls are tumbled in an enclosure, continously, by an air blower. The air flow out of the ball exit tube carries such balls and randomly delivers one at a time upon demand to the game operator who then calls out the letter-number combination thereon.
In games of this type it is difficult to maintain the proper pace in calling out letter-number combinations as the game continues. On the one hand, both the players and operator want the letter-number combinations called out rapidly enough to permit playing of a certain minimum number of games in the course of the available time. On the other hand, sufficient time must be allowed after calling out such letter-number combination for a person of moderate skill to scan and mark a reasonable number of cards. While these two requirements conflict to an extent, random variations in the amount of time allowed between calls insure that neither requirement will be satisfied and may leave the players alternately bored and unable to complete marking of the cards. Yet such randomness in the call interval normally results when the game operator relies on his own "mental clock" as to the time between calls. On the other hand, it is inconvenient, and normally not very reliable to require the human operator to use his wristwatch or a wall clock to determine when to call out the next number, particularly when he is also occupied with operating the ball delivery machine, watching the players, etc.